Preserving the heavenly sound of Stradivarius violins

Strad stringed instruments made in Italy in 17th century by mysterious Antonio Stradivari

Made with Renaissance technology, some musicians say their quality is unequalled today

Strad violins can sell for millions, but are priceless to their players

Cremona, Italy (CNN) -- For virtuoso violinist Anne-Sophie Mutter, only one violin can truly give voice to her prodigious talents -- her Stradivarius. And she likens playing it for the first time to meeting her soul mate.

"It sounded the way I (had) always been hoping," she said. "It's the oldest part of my body and my soul. The moment I am on stage, we are one, musically."

Stradivarius violins -- or "Strads" -- are the instrument of choice for the world's best violinists -- but only a lucky few actually get to play one.

Mutter likens hers to an irreplaceable piece of art. Indeed, it was made by Antonio Stradivari, the greatest-ever luthier, or stringed instrument-maker, who lived from 1644 to 1737.

Ann Sophie Mutter makes guest appearance

Mutter's Strad was crafted in Italy and is at least 250 years old. It has been played by many musicians over the years, including Hungarian violinist Jelly D'Aranyi, for whom famed composer Maurice Ravel wrote his "Tzigane for Violin and Orchestra."

So, what is it that makes a Stradivarius so very special? According to Mutter, it's a question of personal fit; for her, it's the "depths of the colors and the incredible amount of dynamic range" that means it can sing out even in a roaring orchestra, yet also complement the softest pianist.

Stradivarius stringed instruments may be almost priceless to the people who play them, but they are also serious cultural commodities worthy of six figure sums at auction.

Last year, a 1697 Stradivarius violin went under the hammer for a record-breaking $3.6 million. Thought to have once been owned by Napoleon Bonaparte, it was sold to concert violinist Anne Akiko Meyers.

It's the oldest part of my body and my soul. The moment I am on stage, we are one, musically--Anne-Sophie Mutter, virtuoso violinist

As far as Matthew Hunter, a viola player for the Berlin Philharmonic is concerned, putting a price on a Stradivarius is like putting a price on the Sistine Chapel.

"This was made with Renaissance technology," he said of the Strad viola that he plays on loan as director of string ensemble, the Philharmonic Stradivari Soloists. "It was made with hands, wood and metal tools, (and) up to this day nothing has equaled it in quality or beauty."

Not much is known about the man whose talents brought these iconic instruments to life.

It is thought that Stradivari was born in 1644 in Cremona, northern Italy, and was mentored by violin-maker Nicolo Amati. His instruments, which also include violas and cellos, would be inscribed with the Latin version of his name: "Stradivarius."

"No other violin maker has quite the same mystique as Antonio Stradivari," luthier and restorer Bruce Carlson said.

"He was prolific, that's for sure," said Carlson, who studied violin-making in Cremona, where Stradivari lived and worked.

We have the feeling when we're on tour with these instruments that the owners are more concerned about their instruments (than their) own personal safety--Matthew Hunter, viola player, Berlin Philharmonic

"He had very clear ideas of what he was doing, I think. He'd experiment throughout his whole life -- you see little minute changes in his instruments as the years (went) by," Carlson continued.

And as with any highly sophisticated piece of equipment, Strads need to be kept finely tuned.

At the same time every day, in a chapel-turned-museum in Cremona, a musician named Andrea Mosconi plays a selection of fine violins, including a 1715 Stradivarius, in order to keep their unique sound alive.

He says that if they aren't carefully looked after, including being played every day, the wood becomes stiff and unresponsive and the instruments will lose their rich sound.

Indeed, many of the musicians lucky enough to own or play a Strad consider themselves merely the custodians of these precious instruments.

"I feel a great responsibility to pass it on in a perfect condition to the next generation," said Mutter.

It may be daunting at first, but, says Hunter, musicians get used to it. "Now I'm able to get past the idea of doing something really stupid and dropping it or throwing it over my shoulder, or in some way ruining it," he said.

"We have the feeling when we're on tour with these instruments that the owners are more concerned about their instruments and their safety than our own personal safety," he continued.

It's all worth it, though, and if the musician trusts their Strad, it can elevate their music. "There's no point in really forcing the instrument. It can do it all," Hunter said.